The present invention relates to a chromatographic separator and more particularly to the control of circular paths and pumps in an intermittently-moving-bed chromatographic separator and a simulated moving-bed chromatographic separator.
In manufacturing industries such as the sugar industry or the pharmaceutical industry, chromatographic separators are widely used to extract one or more components from fluid of a crude material consisting of a plurality of components and obtained from nature or through chemical reactions. Among the chromatographic separators, a variety of moving-bed separators have been proposed other than the batch fixed-bed separators conventionally used.
FIG. 8 is a schematic cross-sectional view illustrating a separation vessel, showing the principle of a typical chromatographic separator employing the moving-bed scheme. The separation vessel 60 is filled with a filler (adsorbent) 62 in advance, and is full of liquid eluent. A feed liquid material including two species of components A and C is introduced from a feed liquid material supply port F, and the liquid eluent is supplied from a liquid eluent supply port D at a constant linear speed. Each of the components A and C moves at different linear speeds within the separation vessel 60 due to the difference in affinity for the filler. For example, the component A having a lower affinity moves at a higher linear speed, whereas the component C having a higher affinity moves at a lower linear speed. Accordingly, by discharging the circulating liquid from two appropriate positions, the feed liquid material can be separated into a liquid containing more of the component A (hereinafter simply referred to as the component A) and a liquid containing more of the component C (hereinafter simply referred to as the component C).
A chromatographic separator employing the moving-bed scheme creates the movement of the filler, in the direction opposite to the flow of the liquid eluent, at a speed between the speed of movement of the component A and that of the component C. As shown in the figure, this makes it possible to take out the components at respective positions across the supply position of the feed liquid material. That is, as viewed from the direction of the flow of the circulating liquid, the component A can be taken out behind the feed liquid material supply position F and the component C can be taken out in front of the feed liquid material supply position F. In this scheme, since it is difficult to allow the filler to move at a uniform speed, it is rather difficult to use this scheme in any commercial applications.
A separator has been in practical use which is capable of obtaining the separation performance equivalent to that of a separator of the foregoing moving-bed scheme theoretically conceived, without allowing the filler to move. FIG. 9 illustrates the principle of this type of separator. In this scheme, the separation vessel 60 is divided into a plurality of columns 64 (twelve columns in the example of the figure), which are coupled to form an endless circular path. Instead of the movement of the filler, the supply positions of the feed liquid material F and the liquid eluent D and the discharge positions of the components A and C are shifted in the direction of flow of the liquid eluent. As time elapses, the distribution of the liquid in the system is shifted in the direction of the circulating liquid. When the concentration distribution has been shifted by a distance corresponding to one column after a certain period of time, the supply positions of the feed liquid material and the liquid eluent and the discharge positions of the components A and C are shifted in the direction of the circulating liquid by the distance corresponding to one column. The repetition of this operation makes it possible to supply and discharge each of the liquids at the optimum position at any time. Three schemes are employed to shift the supply positions of the feed liquid material and the liquid eluent and the discharge positions of the components A and C. The schemes, now in practical use, include a simulated moving-bed scheme in which liquid injection valves and liquid discharge valves, such as electromagnetic valves, are assembled and switched sequentially; another simulated moving-bed scheme in which a rotary valve having a number of nozzles is used and an intermittently-moving-bed scheme in which a rotary valve having a number of nozzles is used while moving the columns.
To drive a fluid in a chromatographic separator having the foregoing endless circular path, a drive force is typically provided by means of an injection pump for a feed liquid material and an injection pump for a liquid eluent. In addition, a drive force is also provided, for example, by means of one or more circulation pumps disposed in the circular path. Here, it is necessary to maintain the equality between the total amount of the feed liquid material and the liquid eluent, injected into the circular path, and the total amount of components A and C, discharged from the circular path, at any time to prevent a pressure fluctuation in the circular path. Thus, some of the pumps used therein have a constant rate property, and in some cases, a flow rate control mechanism is employed in addition thereto. However, the pump having the constant rate property or the flow rate control mechanism is expensive, and thus the cost for the chromatographic separator increases.
Furthermore, many of the separators employ back pressure regulating valves, which are adapted to open when the pressure of the circular path has been increased, in order to keep the pressure of the circular path at a specified value with accuracy. For example, these values are used in the discharge lines for the component C. In this case, the pressure within the circular path system is not lower than the one that is set for the back pressure regulating valves, thus necessitating columns or pumps which are capable of withstanding this pressure. Use of the columns and pumps having such a pressure specification further raises the cost of the chromatographic separator.
In view of the above, it is an object of the present invention to reduce a number of pumps in a chromatographic separator which employs the simulated moving-bed scheme or the intermittently-moving-bed scheme, and at the same time to reduce pressure in the circular path by eliminating the back pressure regulating valve, while keeping the pressure of the circular path at a specified value, thereby reducing the equipment cost of the chromatographic separator while allowing the separation performance thereof to remain unchanged.
The present invention provides, in a preferred embodiment is thereof, a chromatographic separator including: at least four columns consecutively coupled together to form a circular path for circulating a liquid mixture by coupling an outlet port of one of the columns to an inlet port of an adjacent one of the columns, the circular path having a first injection port for introducing a feed liquid material including at least first and second components, a second injection port for introducing an liquid eluent, a first discharge port for discharging the first component and a second discharge port for discharging the second component; a port switching member for sequentially switching the first and second injection ports and the first and second discharge ports toward downstream of the circular path; first and second pumps having delivery ports coupled to the circular path via the port switching member at respective positions in association with each other; a first selector valve having a first select position for connecting the first pump in the circulating path and a second select position for allowing the first pump to inject the feed liquid material; and a second selector valve having a third select position for connecting the second pump in the circulating path and a fourth select position for allowing the second pump to inject the liquid eluent.
In accordance with the chromatographic separator of the present invention, movement of the liquid mixture (a circulating liquid) containing the feed liquid material and the liquid eluent in the circular path, injection of the feed liquid material and the liquid eluent into the circular path, and discharge of the first and second components from the circular path can be performed by switching the first selector valve and the second selector valve and driving the first and second pumps. Accordingly, the number of pumps employed in the chromatographic separator can be reduced down to two. In addition, each component can be discharged by means of ordinary valves without using a back pressure regulating valve, thereby allowing the pressure specification within the circular path system to be reduced.
The chromatographic separator according to the present invention is applicable to any one of the simulated moving-bed chromatographic separator and the intermittently-moving-bed chromatographic separator.